1. Field of the Invention
The invention relates to a pressure sensor measuring element for a pressure sensor for the detection of pressure in a combustion space of an internal combustion engine during the operation of the latter, with a separating diaphragm, with a plunger for the transmission of deflections of the separating diaphragm to a force measuring element, and with a sleeve which receives the plunger and which is closed by means of the separating diaphragm at a first end intended to face the combustion space and is designed for carrying the force measuring element at the opposite second end. The invention relates, moreover, to a pressure sensor, provided with such a pressure sensor measuring element, for measuring the combustion space pressure in an internal combustion engine by means of such a pressure sensor measuring element.
2. Background Information
Such a pressure sensor and such a pressure sensor measuring element are known from EP 1 255 099 81. This publication will be dealt with in more detail hereafter.
U.S. Pat. No. 4,382,377 A describes a pressure sensor for an internal combustion engine in order to measure the internal pressure there in a combustion space. For this purpose, the known pressure sensor has a sensor outer housing which can be screwed into a threaded bore of a combustion chamber wall (that is to say, for example, a cylinder head). At the first end intended to face the combustion space, the sensor outer housing is closed by means of a separating diaphragm which can be deflected by the combustion space pressure. The separating diaphragm is produced in one piece with the sensor outer housing. The deflection of the separating diaphragm is transmitted via a plunger, which is guided directly inside a slender threaded region of the sensor outer housing, to a second end which faces away from the combustion space and where a force measuring element converts the longitudinal movement of the plunger into pressure signals. The pressure sensor thus has a very simple set-up, the sensitive force measuring element being accommodated in a protected region outside the high combustion space temperatures. For this purpose, the plunger is produced from a ceramic having poor thermal conductivity. However, such a pressure sensor may have considerable temperature dependencies, since the sensor housing may expand differently in relation to the plunger in the case of the temperature gradients which prevail on the combustion space wall. Moreover, loads exerted upon the sensor housing when the latter is being screwed in, this being carried out with appreciable torque for the purpose of gas-tightness, may lead to a falsification of the plunger deflection and therefore to errors in pressure measurement.
A comparable set-up of a combustion space pressure sensor with a metal or ceramic plunger guided directly in a sensor housing is known from U.S. Pat. No. 5,703,282 A. In this case, however, the separating diaphragm is not produced in one piece with the sensor housing, but instead is welded to that end of the latter which is on the combustion space side so as to hermetically close this end. A comparable set-up is also to be found in U.S. Pat. No. 5,199,303 A.
In order to mitigate the abovementioned temperature dependencies, the pressure sensor for combustion spaces of internal combustion engines according to the initially mentioned EP 1 255 099 B1 was proposed. In this case, the sensor outer housing has arranged inside it a separate pressure sensor measuring element having a sleeve which forms a spacer element and in which the plunger is guided. This sleeve is fastened with its first end intended to face the combustion space to the sensor outer housing. The sleeve is not fastened at the second end lying internally and there carries a force measuring element to which the deflection of the separating diaphragm is transmitted by means of the plunger. Both the plunger and the sleeve are manufactured from ceramic in order to block the high combustion space temperatures and also temperature shocks. This combustion space sensor functions very well and has proved appropriate in practice. However, it is relatively costly to produce.